全球GPS矢量场的分区描述及规律性分析

以平均选择的GPS站点运动年速率编制了全球板块运动矢量场,从而揭示了以下几点规律:1从北大西洋洋脊东侧起,直至西北太平洋岛弧带,欧亚大板块总体呈现顺时针宽弧形运动;2从北大西洋洋脊西侧直至美洲大陆西边缘,北美大板块呈现反时针宽弧形运动;3从南大西洋洋脊东侧起,直至克马德克—新西兰一线,非洲板块和印—澳板块一并呈现从北东指向渐变为北北东指向的运动;4东南太平洋洋脊西侧太平洋板块总体向北西西方向运动;5东南太平洋脊东侧海底大小板块总体向北东东运动;6南美洲整体向北运动;7北极区总体向太平洋北缘运动;南极洲总体向大西洋区运动,并有分裂—对旋迹象。分析上述运动的分区展布,可推论以下几点运动动力学的认识:1拖动全球板块一级运动势态的地幔流可分解为由南极区向北的径向流与由大西洋洋脊和东南太平洋洋脊的东西两侧纬向流的二元动力联合作用,从而造成全球性指向北东和北西的斜向运动;2以重力大地水准面所展现的低阶双重非对称的地球,是引导表壳发育张裂洋脊带和汇聚俯冲带的力学条件;3沿赤道两侧不协调运动带呈现压扭、张扭的复杂变动除了南半球与北半球地幔流在运动指向和速度的差异而造成之外,还可能与地球质心的偏心和南、北半球自转速度的差异变化有关;4南极洲相对环南极洋脊的偏极分流运动还有待进一步研究。在以上认识的基础上,本文讨论了造成三大洋脊在全球表壳的分布、全球深俯冲带仅仅在环太平洋边缘带内发育、北半球和南半球的板块径向、纬向运动有整体性差异等问题的原因。造成上述现象是与地球整体的双重不对称性有关,即北、南半球和0°/180°半球的缩、胀和快、慢的双重非对称,而这种双重不对称性是地球内部物质的热状态、运动状态以及质量分布等原因造成的,我们认为以重力大地水准面所展现的低阶双重非对称的地球表壳,既是约束地幔流的上边界条件,又是引导表壳发育张裂带的力学条件,目前地球表面的这些一级构造因素并不是随意造成的,它们有着深刻的地球物理背景。本文还着重讨论了双重非对称畸形壳体的构造力学背景,根据GPS资料建立了地球热流驱动的地幔经、纬向一级对流格局。     

1978-2004年天津城市空间形态的时空变化

Taken fractal dimension, compact ratio, urban centroid and urban principal axis as the urban spatial characteristic indices, Tianjin city’s urban area is investigated in the last 26 years in a quantitative perspective, and its traits and changes during different periods are also analyzed. It is clear that these indices can not only scientifically and explicitly assess the urban morphology, urban direction and its changes and trends, but also uncover long-term effects of economy and urban planning on urban morphology.     

Estimating quality factor from surface seismic data: A comparison of current approaches

The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried.     

星载SAR测量海洋流场研究进展

多普勒信息是合成孔径雷达（SAR）进行海洋动力遥感的一个重要参数,自从20世纪80年代末就已经开始利用该参数反演海表面动力过程的相关研究.本文重点论述了星载SAR多普勒信息反演海表面流及其应用研究,主要包括SAR干涉测量方法获取海洋流场信息的主要技术手段及研究进展;多普勒频移方法反演表层海洋流场的发展历程及在上层海洋现象（包括地转流、准地转流以及中小尺度过程）中的应用研究;相关的国外重要数据融合计划和研发计划.目前国内在海洋流场的遥感方面还处于起步阶段,重点关注于反演理论和方法,而将反演信息应用于上层海洋动力的研究,还十分缺乏.希望通过本文的综述,为后续在该方向的研究提供借鉴.     

Synoptic Characteristics Related to Warm-Sector Torrential Rainfall Events in South China During the Annually First Rainy Season

Warm-sector torrential rainfall (WSTR) events that occur in the annually first rainy season in south China are characterized by high rainfall intensity and low radar echo centroids. To understand the synoptic characteristics related to these features, 16 WSTR events that occurred in 2013-2017 were examined with another 16 squall line (SL) events occurred during the same period as references. Composite analysis derived from ERA-Interim reanalysis data indicated the importance of the deep layer of warm and moist air for WSTR events. The most significant difference between WSTR and SL events lies in their low-level convergence and lifting; for WSTR events, the low-level convergence and lifting is much shallower with comparable or stronger intensity. The trumpet-shaped topography to the north of the WSTR centers is favorable for the development of such shallow convergences in WSTR events. Results in this study will provide references for future studies to improve the predictability of WSTR.     

用质心跟踪法预报强对流天气的试验研究

利用１９８７－１９９１年６－８月间影响北京地区的１３次西北路径强对流天气过程数字化雷达回波资料，用质心跟踪法，分别对不同强度等级廓线的飑线回波带整体，和选择其中对预报地区有影响的快（条）状回波，作移动客观外推预报试验及分析。结果表明，质心跟踪法对强对流雷达回波具有较好的客观外推预报能力。其中，有选择的块（条）状回波的移动外推预测效果比飑线回波带整体要好，而两者又均以不衰减的回波区外推预报效果最好，     

利用多级弦长弯曲度复函数构建复杂面实体综合形状相似度量模型

介绍了一种复杂带洞面实体空间对象的几何相似度度量方法。该方法提取面实体的中心距离、轮廓线的多级弦长、弯曲度及凸凹性等特征,构造多级弯曲度半径复函数对其局部和整体特征进行描述,并通过傅里叶变换得到傅里叶形状描述子对面实体间的形状相似性进行度量。同时根据场景完整度和相似性度量模型计算复杂带洞多边形中每个场景的匹配度,利用多级特征完成复杂面实体间的几何相似性度量。对不同空间复杂度的面实体的几何相似性的度量试验表明,该方法简单可行且不失精度,结果符合人类认知。     

超大视场太阳敏感器图像质心提取算法

太阳图像质心提取是利用太阳敏感器进行天文导航的关键技术之一,直接决定了太阳敏感器的观测精度。针对超大视场太阳敏感器非圆形太阳图像质心提取问题,首先提出像面椭圆拟合算法,较好地解决了椭圆及近似椭圆形太阳图像的质心提取问题,然后进一步提出了球面圆拟合算法。该算法根据相机的投影和畸变模型,将太阳图像的边缘点映射到物方空间,对物方空间的边缘点进行球面圆拟合,从而确定太阳质心位置。在估计球面圆拟合算法的精度时,需要将太阳质心位置映射回像面。理论上,球面圆拟合算法不再需要顾及太阳图像的形状,算法更为严谨。将椭圆拟合算法和球面圆拟合算法应用到实测的太阳图像质心提取中。结果表明,椭圆拟合算法更适合处理半视场角70°~80.3°的太阳图像,平均精度约为0.075pixels;球面圆拟合算法更适合处理半视场角大于80.3°的太阳图像,平均精度约为0.082pixels。     

沿海城市天津湖泊—内涝时空变化耦合关系

近年来城市内涝问题凸显,给社会生产和人们生活带来诸多不便。以天津市为例,基于Landsat系列数据,利用MBWI水体指数法逐年提取其1984年—2017年的湖泊数据,并结合内涝点数据,研究天津市湖泊空间演变与内涝耦合性,建立湖泊演变系统与内涝系统的综合评价指标体系,构建湖泊演变与内涝之间的耦合度模型。结果表明:天津市湖泊面积在1984年—2005年波动上升,2005年—2017年间断减少,减少原因主要是人为干扰。2005年—2017年东丽区的湖泊面积减少最快且幅度最大。同时,大部分区的湖泊面积占比大幅降低;天津市的内涝区主要分布在市内6区及附近区,其中无湖泊区域比有湖泊区域容易产生内涝,湖泊面积小的区域比湖泊面积大的区域容易产生内涝。湖泊面积占比越小,内涝点密度越大。天津市湖泊群质心整体由中心向四周移动,湖泊质心移动的反方向容易产生内涝。湖泊演变与内涝之间存在初级耦合协调关系。     

质心分析法在小沙洲动态演化分析中的应用--以江苏辐射沙洲亮月沙为例

在遥感(RS)、GIS技术的支持下，根据1973—2000年江苏盐城幅卫片，对江苏辐射沙洲外围小沙洲的动态趋势研究方法进行了探讨。在小沙洲轮廓边缘叠合比较的基础上。引入了形态学中质心的概念，并将之运用到辐射沙洲北部的亮月沙沙洲中。研究结果表明：(1)通过对外围小沙洲进行质心分析，可较好地揭示小沙洲的动态变化趋势。(2）亮月沙在整体南退的趋势下，同时还叠加了较为明显的东西摆动韵律，共可分为6个阶段。本文还对亮月沙动态变化趋势原因进行了讨论。